Collateral Estoppel is a legal doctrine that prevents a party from relitigating an issue that has already been decided in a previous case. This means that if a court has made a final ruling on a specific fact or issue, that ruling is binding in future cases involving the same parties, even if the new case involves different claims. The purpose of Collateral Estoppel is to promote judicial efficiency and consistency by avoiding repetitive litigation over the same issues. It helps ensure that once a matter has been settled, it remains settled, thereby protecting the integrity of the judicial system.